A method and apparatus for locating the source of noise ingress into a CATV system return path by coupling a filter having a passband in the noise frequency bandwidth to the nodes between adjacent return path amplifiers. The filter is sequentially coupled to the nodes, working away from the CATV system headend. A signal level meter or the like monitors the effect on the noise of coupling the filter to the nodes. When a node is reached at which coupling of the filter to the node no longer has any effect on the signal level in the node, the source of the noise is isolated in the node immediately preceding the node under test.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for detecting the source of noise in a CATV circuit, the CATV circuit comprising a plurality of amplifiers, each amplifier having a first, input port and a second, output port, a node coupling the second port of a respective amplifier to the first port of the next adjacent amplifier in the circuit, the method comprising the steps of proceeding along the circuit away from the CATV circuit headend from node to node, determining at each node whether the noise is present, reaching a node at which the noise is not present, and determining that the noise source is in the node tested immediately preceding the node at which the noise is not present.
2. The method of claim 1 wherein the step of determining at each node whether the noise is present comprises the steps of providing a first filter having a passband including the noise frequencies, coupling the first filter to the node, and determining the effect on the noise of coupling the first filter to the node.
3. The method of claim 2 wherein the step of providing a filter having a passband including the noise frequencies includes the step of providing on the filter a third port for coupling to an instrument for measuring signal strength, the step of determining at each node whether the noise is present further comprising coupling the instrument to the third port and measuring the strength of the noise at the third port.
4. The method of claim 3 wherein the step of providing a first filter having a passband including the noise frequencies comprises the step of providing a first filter having a passband including the noise frequencies and a first characteristic impedance in the passband.
5. The method of claim 4 wherein the step of determining at each node whether the noise is present further comprises the step of providing a second filter having a passband including the noise frequencies and a second characteristic impedance in the passband, coupling the second filter to the node, and determining the effect on the noise of coupling the second filter to the node.
6. The method of claim 5 wherein the step of coupling the first filter to the node and the step of coupling the second filter to the node together comprise the steps of alternately coupling the first and second filters to the node.
7. The method of claim 6 wherein the second filter is coupled to the third port, the step of determining at each node whether the noise is present further comprising comparing the strength of the noise with the first filter coupled to the node and the strength of the noise with the second filter coupled to the node.
8. The method of claim 2 wherein the step of providing a first filter having a passband including the noise frequencies comprises the step of providing a first filter having a passband including the noise frequencies and a first characteristic impedance in the passband, the step of determining at each node whether the noise is present further comprising the step of providing a second filter having a passband including the noise frequencies and a second characteristic impedance in the passband, coupling the second filter to the node, and determining the effect on the noise of coupling the second filter to the node.
9. The method of claim 8 wherein the step of coupling the first filter to the node and the step of coupling the second filter to the node together comprise the steps of alternately coupling the first and second filters to the node.
10. The method of claim 9 wherein the second filter is coupled to the third port, the step of determining at each node whether the noise is present further comprising comparing the strength of noise with the first filter coupled to the node and the strength of the noise with the second filter coupled to the node.
11. Apparatus for detecting the source of noise in a CATV circuit, the CATV circuit comprising a plurality of amplifiers, each amplifier having a first, input port and a second, output port, a node coupling the second port of a respective amplifier more downstream in the CATV circuit away from the headend to the first port of the next adjacent amplifier more upstream in the CATV circuit toward the headend, the apparatus comprising a first filter having a passband including the noise frequencies, at least a first conductor for coupling the first filter to the node, and an instrument for determining the effect on the noise of coupling the first filter to the node.
12. The apparatus of claim 11 wherein the first filter comprises a third port and the instrument comprises a signal strength meter, the apparatus further comprising at least a second conductor for coupling the signal strength meter to the third port.
13. The apparatus of claim 12 wherein the first filter further comprises a first filter having a first characteristic impedance in the passband, the apparatus further comprising a second filter having a passband including the noise frequencies and a second characteristic impedance in the passband, and at least a third conductor for coupling the second filter to the node.
14. The apparatus of claim 13 and further comprising a switch for alternately coupling the at least first conductor and the at least third conductor to the node.
15. The apparatus of claim 14 and further comprising at least a fourth conductor for coupling the second filter to the third port.
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July 29, 1997
September 18, 2001
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